1. Technical Field
The present invention relates to an insertion system for release of a self-expanding stent device in a body vessel, comprising a first grip, which is fixedly connected to a shaft, a second grip, which is mounted on the shaft to be movable in axial direction, a sheath, which, in a distal portion thereof, keeps the stent device radially compressed and which is fixedly connected to the second grip, and a retention element, which is fixedly connected to the shaft and is guided in the sheath, wherein the retention element holds the stent device in its axial position relative to the first grip when the sheath is being retracted.
2. Background Art
Insertion systems and stent devices of this kind are known, for example, from U.S. Pat. No. 5,026,377 A.
With such insertion systems, stent devices are implanted into blood vessels for the treatment of damages in blood vessels like, for example, aneurysms. Such treatment is applied, for example, in the surgical reconstruction of major blood vessels, for example the descending part of the thoragic aorta, that cannot be treated by conventional surgical methods because of insufficient accessibility. Examples of indications which are to be treated in this way, and as a result of which the function of the vessels is greatly impaired or there is a danger of rupture of the vessels, include blood vessel damage caused by disease or the like, acquired or congenital aneurysms or partial occlusions of the lumen of a blood vessel, for example by formation of pseudolumina.
Various implantable stent devices are known by means of which blood vessels, for example arteries, are kept open or widenings are excluded from the blood stream. These include stents and stent grafts.
Stents generally comprise a tubular body which is inserted into the vessel and is expanded and fixed at the appropriate site in order to keep open the lumen of the vessel.
Stent grafts comprise, for example, a series of stents or, respectively, a wire framework made of a self-expanding material. In this context, stents are understood to be individual self-expanding elements. The self-expanding elements or, respectively, the wire framework are connected to each other by a textile or PTFE tube, called a graft sleeve, to form a functional unit and in this way, analogous to the stents described above, they form a tubular body that supports the vessel walls.
Further, stent devices are known which, in addition to a stent graft, also comprise a woven prosthesis part, a so-called prosthesis cuff, attached to the proximal end of the stent graft.
Here, and also in the text below, “proximal” designates as usual a side directed towards the user (operator), and “distal” designates a side directed away from the user.
Such a prosthesis cuff enables a secure surgical fixation of the stent device to the vessel wall and, by virtue of its relative flexibility, can be used as a vessel adapter for connecting an implanted stent graft to other vessel reconstruction implants or to a vessel itself, for example in vascular reconstruction of the aortic arch.
In the principle described in U.S. Pat. No. 5,026,377 A mentioned at the outset, the insertion system has a first grip, which is fixedly connected to a proximal end of a shaft. Further, a second grip, which is fixedly connected to a sheath, is arranged movably on the shaft. Here, “fixedly” means that the connection between second grip and sheath is suitable for taking up tension, compression and torsion forces. Arranged between sheath and shaft there is a stent device, which is disposed inside the sheath and is radially compressed by the latter. The cross-section of the stent device is in this way greatly reduced, and it can be easily inserted into a vessel. When the sheath is then retracted relative to the stent device by a movement of the second grip, the stent device, by virtue of the resiliency of the metal frame or metal stent, expands back to its original shape in the portion of the stent device released from the sheath. The sleeve surface of the stent device is thereby stretched out and wedges itself within the blood vessel.
For implantation, the stent devices are first inserted into the blood vessel with the aid of catheters, which are advanced through the vessel lumen, and they are positioned at the correct location in the vessel. In this context, “deployment position” is understood as the whole area of a vessel filled by a stent device after expansion thereof. The term “landing zone” is understood as a short proximal area of the deployment position at which the stent device is surgically connected to the vessel wall after expansion.
By contrast, the “deployment zone” designates the area of the insertion system at whose axial level, after expansion, the part of the stent device is located which is to be surgically connected to the vessel wall. In the case of an insertion system loaded with a non-foreshortening stent device, the deployment zone is accordingly situated at the axial level of a proximal portion of the stent device compressed in the sheath. In the case of an insertion system with a non-foreshortening stent device having a prosthesis cuff portion provided at its proximal end, the deployment zone can be offset in proximal direction, relative to the proximal end of the stent device compressed in the sheath, to such an extent that it corresponds to the position of the distal portion of the prosthesis cuff after the expansion and unfolding of the stent device, if the stent device is to be connected to the vessel wall at the distal end of the prosthesis cuff portion after the expansion and subsequent unfolding of the prosthesis cuff portion.
By contrast, in the case of an insertion system with a foreshortening stent device, the deployment zone can be offset in distal direction, relative to the proximal end of the stent device compressed in the sheath, to such an extent that it corresponds to the position of the proximal portion of the stent device in its unfolded state.
The correct position of the stent device can be monitored, for example, by X-ray markers. However, the continuous monitoring of the position by X-ray markers exposes the operator and patient to a certain amount of radiation. Particularly in operations performed on an openly accessible aortic stump, in which the landing zone for the stent is directly visible with the naked eye, for example in procedures on the thoracic part of the descending aorta, continuous monitoring of the position by X-ray markers is therefore not only an unnecessary risk but also extremely complicated, since there is no blood flow. This is because the patient is connected to a heart-lung machine during these operations such that the diseased vessel can be opened, because it is empty of blood.
In the context of transluminal treatment of blood vessels, a number of other techniques for positional control of a stent device or of another medical device are known, which techniques do not or only to a minor extent employ X-radiation.
For example EP 1 943 988 A1 describes an insertion system for a stent device, in which positional control of the stent device is achieved by sensors provided on the insertion system or the stent device. These sensors operate on the basis of non-ionizing radiation, magnetic fields or pressure waves.
EP 1 391 181 A1 describes an apparatus for virtual endoscopy, in which apparatus the position of a surgical instrument is determined by means of sensors provided on the surgical instrument, and the data acquired are transmitted to an imaging system for generating a virtual representation of the patient's body and the surgical instrument inserted therein.
DE 10 2005 059 261 A1 describes a catheter device for the treatment of a vessel obstruction, which catheter device has one or more sensor systems provided on its distal end, for image recording and three-dimensional gauging of the vessel to be treated.
These techniques and devices, however, have the disadvantage that they require expensive equipment, which as well is generally very sensitive to technical failure and sensing errors resulting, for example, from external cues. For instance, metallic objects in the vicinity of the operation field might disturb magnetic fields used for determining the position of the medical device.
Further, the technical complexity of the sensor systems results in high production costs, hence being especially disadvantageous in single-use surgical instruments such as insertion devices for stent devices.
After the stent device has been positioned in the vessel, according to the teaching of U.S. Pat. No. 5,026,377 A mentioned at the outset, the sheath is retracted in the proximal direction. In this process, the stent device lies in contact with a retention element, which holds the stent device in its axial position relative to the first grip while, with the aid of the second grip, the sheath also enclosing the retention element is pulled off from the stent device to permit expansion thereof.
When a self-expanding stent device is released in this way, the operator often has to exert a considerable force on the second grip, connected to the sheath, and on the first grip, connected to the shaft and to the retention element.
During this process, the large amount of force to be applied is mainly caused by friction between the outer wall of the stent device, strongly compressed against its expansion forces, and the inner wall of the sheath.
When pulling back the sheath, the operator, at the same time, has to take care not to shift the stent device axially away from the site at which it is intended to be specifically placed.
In this connection, various methods, stent devices and stent insertion systems are known, for example from EP 1 923 024 A2 or EP 1 440 672 A1, in which shifting of the stent is intended to be avoided by anchoring of the stent in the vessel wall in good time.
However, a disadvantage of this is that, for example with stent parts penetrating into the surrounding vessel wall, additional trauma may be caused. Moreover, the known methods and devices do not offer any certainty of a proximal portion of the stent device coming into contact with the vessel wall at its predetermined landing zone. Consequently, in the event of incorrect handling by the operator, the stent device may shift out of position, for example in distal direction, which in some circumstances is associated with the formation of folds, for example in a graft sleeve. Such folds pose an additional risk in the area of the inner wall of a stent device that has been inserted in this way. Secure anchoring of the proximal end in the vessel wall is also made more difficult, and the imprecision of the proximal deployment position may compromise the overall success of the operation.
During the course of the operation, this shifting of the stent device as a whole, or at its proximal end or distal end, can be avoided by not moving the stationary parts of the stent insertion system, especially the shaft and the first grip, relative to the deployment position, such that the deployment zone remains unchanged in position relative to the landing zone.
In the known stent insertion systems, the operator can ensure the unchanged position of the stent device relative to the body vessel, and, therefore, relative to the axial deployment position, only by precisely controlling the hold on the first grip of the stent insertion system. However, since he at the same time has to use his other hand on the second grip to carry out the withdrawal movement, there is a high probability of the withdrawal movement, or of compensatory movements in the opposite direction, causing the stent device to shift, at least partially, in axial direction relative to the predetermined landing zone. This shifting may compromise the success of the operation or even cause damage to the vessel wall.